Some time ago I mentioned I could not figure out for the life of me why I couldn't get my blankety-blank F4 engine to run properly. After a lot of work I found out the rebuilt YF carburetor purchased from Kaiser-Willys had an undersize main jet. After a couple of tries of drilling it out about another three thousanths in diameter, it runs fine! It came from the rebuilders running too lean. Nice to have my Jeep back!